1. Field of the Invention
The present invention relates to semiconductor packaging technology, and more particularly, to a semiconductor chip package having a tape circuit substrate with beam leads.
2. Description of the Related Art
With the current trend of high integration in semiconductor devices, semiconductor packaging and interconnect technologies are becoming very important. Moreover, as market demand for mobile handsets and liquid crystal displays (LCDs) increases, there will be a growing demand to make the semiconductor chip packages smaller, thinner, lighter, and more multifunctional. To meet this trend, several types of semiconductor packages using a tape circuit substrate have been developed and introduced. For example, a tape carrier package (TCP), a chip-on-film (COF) package, a micro ball grid array (μ-BGA) package and so on fall within these package types.
In general, a semiconductor chip package having a tape circuit substrate uses what is called a TAB (tape automated bonding) technique to establish a connection between an integrated circuit (IC) chip and the tape circuit substrate. A typical package using the tape circuit substrate is shown in FIGS. 1A and 1B. FIG. 1A is a plan view and FIG. 1B is a cross-sectional view taken along the line IB—IB of FIG. 1A.
Referring FIGS. 1A and 1B, a conventional semiconductor package 100 is shown to include an IC chip 20. The IC chip 20 has a large number of chip pads 21 formed on the top surface thereof. A chip bump 22 is formed on each chip pad 21. A tape circuit substrate 10 has a base film 11, a large number of beam leads 12, and a protective layer 13. The base film 11 is made of a polyimide, having a rectangular opening 14 formed at central portions. The chip bumps 22 on top of the IC chip 20, is exposed through the opening 14 of the base film 11. The beam leads 12, which are made of copper, are formed on the bottom surface of the base film 11, and their ends are protruded into the opening 14. The protective layer 13, which can be made of a solder resist material, is formed on the bottom surface of the base film 11 to cover the beam leads 12.
The ends of the beam leads 12, which as previously mentioned are protruded into the opening 14, are bonded onto the chip bumps 22, respectively, using mechanical pressure at a temperature of about 500° C. This is widely known as an inner lead bonding (ILB) process of the TAB technique. Unlike a wire bonding technique, the ILB process of TAB technique has the advantage of allowing gang bonding between the chip pads 21 and the beam leads 12. After the ILB process is completed, a sealing resin 23 encapsulates the top and side surfaces of the IC chip 20 as well as the protruded beam leads 12.
Unfortunately, the typical package 100 discussed above has a reliability problem due to differences in the coefficient of thermal expansion (CTE) between components of the tape circuit substrate 10. As described above, the tape circuit substrate 10 is composed of the polyimide base film 11, the copper beam leads 12, and the solder resist protective layer 13, each having different CTEs of about 20 ppm/° C., about 17 ppm/° C. and about 160 ppm/° C., respectively. Therefore, as depicted in FIG. 2, these components expand due to heat at different rates during the ILB process, which incorporates high temperature and high pressure. This causes thermal mechanical stress (S) in the beam lead 12 bonded to the chip bump 22, resulting in a crack or a break at the bended portion 12a of the beam lead 12. This type of unfavorable defect is also illustrated in FIG. 3.